How to repair a cracked cornice

MitchellMc

Difficulty: Beginner

Cornices conceal the joint between a ceiling and a wall and add a decorative element.

It’s common for cornice mouldings to crack or get damaged over time. This can be unsightly and potentially dangerous.

Here is a simple guide to repairing a cracked cornice using a multi-purpose sealant.

As this project involves chemicals and power tools, please follow all safety guidelines provided by manufacturers and use the recommended safety gear.

Let us know if you have any questions. We’d be happy to assist.

Steps

Step 1

Open the gap.

Use a scraper to open the gap or crack between the cornice and wall so that you create space for sealant. Without a gap, the sealant would only be applied to the surface and any new movement would split the cornice again.

Scrape off the paint at any points along the crack where the cornice is still attached to the wall and remove any loose debris.

Do this until you can fully insert the scraper behind the cornice.

1.1 Cracked and seperated cornice.png 1.2 Opening gap between cornice and wall.png 1.3 Removing debris from gap.png

Step 2

Remove any remaining debris behind the cornice.

Insert wedges in the crack by tapping them in place with a hammer.

Place a wedge every 300mm along the crack to keep it open. Be careful not to drive in the wedges too far as this could cause the cornice to crack further.

Now use your scraper to remove any remaining debris caught behind the cornice.

2.1 Tapping wedges into gap.png 2.2 Wedges in place and gap opened.png 2.3 Removing debris from gap.png

Step 3

Glue the cornice to the wall.

Insert your sealant cartridge into the caulking gun. Place the nozzle behind the cornice and fill along the length of the crack.

Now remove the wedges. Use a rag to remove any excess sealant that may have leaked from the crack.

3.1 Caulking sealant behind cornice.png 3.2 Wedges removed.png 3.3 Cleaning excess sealant.png

Step 4

Screw the cornice to the wall.

Use a drill driver to pre-drill countersunk holes every 15cm along the bottom edge of the cornice. Make sure you are wearing personal protective equipment (PPE), including gloves and safety glasses.

Avoid placing holes too close to the edge. This can cause the cornice to crack.

Now insert screws in the holes and drive them into the wall.

4.1 Pre-drilling and countersinking holes.png 4.2 Screw hole drilled.png 4.3 Screwing through cornice in wall sheet.png 4.4 Screw installed.png

Step 5

Seal the crack.

Tape the area above and below the crack. Use the caulking gun to apply sealant along the crack in between the tape lines.

Now wet your finger in soapy water and use it to smoothen the sealant.

Remove the tape about two minutes after applying the sealant. Do not allow the sealant to dry before removing the tape or you might remove the sealant with the tape.

5.1 Applying tape to both sides of crack.png 5.2 Apply sealant on crack.png 5.3 Smoothing sealant with finger.png 5.4 Sealant smoothed.png

Step 6

Fill the screw holes.

Use your caulking gun to fill the screw holes with sealant.

Smoothen the sealant with a wet finger, as in the previous step.

Allow the sealant to dry for at least an hour.

6.1 Filling screw holes.png 6.2 Smoothing filled holes.png

Step 7

Paint the cornice.

Paint over the repaired area for a smooth finish. This will also help ensure the repaired area blends seamlessly with the rest of the cornice.

You have now repaired your cracked cornice.

7.1 Painting cornice.png 7.2 Repaired cornice.png

Materials

Ceiling paint
3-in-1 silicone sealant
Painter's tape
Plastic wedges
Plaster screws.

Tools

Hammer
Caulking gun
Drill driver
Paint scraper
Paintbrush
Rag
Safety gear, including gloves and safety glasses.

Images

1.1 Cracked and seperated cornice.png 1.2 Opening gap between cornice and wall.png 1.3 Removing debris from gap.png 2.1 Tapping wedges into gap.png 2.2 Wedges in place and gap opened.png 2.3 Removing debris from gap.png 3.1 Caulking sealant behind cornice.png 3.2 Wedges removed.png 3.3 Cleaning excess sealant.png 4.1 Pre-drilling and countersinking holes.png 4.2 Screw hole drilled.png 4.3 Screwing through cornice in wall sheet.png 4.4 Screw installed.png 5.1 Applying tape to both sides of crack.png 5.2 Apply sealant on crack.png 5.3 Smoothing sealant with finger.png 5.4 Sealant smoothed.png 6.1 Filling screw holes.png 6.2 Smoothing filled holes.png 7.1 Painting cornice.png 7.2 Repaired cornice.png